Shoe stiffener manufacture



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[.alntetene UNl'Inuv a [A1155 PATENT v OFF/ICE" snon s'rmrnmm MANUFACTURE Stanley P. Lovell, Newton, Mass., assignor to Beckwith Manufacturing Company,

Dover,

N. H., a corporation of New Hampshire No Drawing. Application March 5, 1935, v Serial No. 9,384

8 Claims.

'I'hisinvention relates to the art of shoe stiffener manufacture, dealing more particularly with the so-called box toe stiffener used to reinforce the forepart of the shoe upper and to maintain its lasted shape during service. Y

One form of stiffener blank in wide vogue at the present time consists of a fibrous base or sheet carrying nitrocellulose or compounded nitrocellulose, such as celluloid, as the stiffening or poten- 10 tial stiffening agent therefor. Such a stiffener blank is dipped into a volatile nitrocellulose S01.- vent in the shoe factory just before the blank is incorporated into the shoe upper and the assembly is subjected to the pulling-over operation, by

which operation the blank can be conformed nice- 1y to the shape of the last while the stiffening agent is in gelatinized condition and can. be allowed to rigidify or set in its conformed shape as the volatile solvent evaporates.

In making a shoe stiffener containing nitrocellulose as the stiffening agent, it is important that the stiffener be quickly and substantially uniformly permeated by nitrocellulose solvent so that when dipped into such solvent it acquires at once the desired plasticity or moldability for the lasting operation. It is also highly desirable to eliminate the fire and explosion hazard presented more especiallyin shipping and storing large quantities of such stiifeners on account of their high nitro- 80 cellulose content.

The foregoing objectives have been sought fruit- 1 lessly for a good many years but are achieved by the present invention. Before delving into a discussion of thepresent invention, it is well to 85 observe that as well as attaining the foregoing objectives one must provide a manufacturing process competitive economically with those currently employed andproductive of v a product whose other significant qualities, including flexi- 40 bility, resiliency, freedom from chemicals noxious to the foot or to handling, capability of being skived, etc, compare favorably with those of the prior art product.

, In producing shoe stiifeners containing nitrocelluolse as the stiffening agent, it has heretofore been the practice to impregnate the fibrous base i with a solution of the nitrocellulose, to dry the impregnated sheet, and to cut the dried sheet into the stiffener blanks. Such practice, although w economical, leads to a product which, besides being highly inflammable, iswithout the desired high porosity or permeability to nitrocellulose solvents. In attempting to overcome the deficiencies of such practice, I have added various chemicals to the bath of nitrocellulose solution through which the fibrous base is run for the purpose of becoming properly impregnated. 'Inadding these chemicals, my aim was to realize a product of low combustibility and appropriate residual porosity or permeability to nitrocellulose solvents. How ever, alkaline fireproofing chemicals were found to be generally objectionable in that they caused undue thickening or gelling of the nitrocellulose solution; neutral fireproofing chemicals generally tended to separate out from the suspension in the solution, also to filter out or deposit on the surface of the fibrous base, and to impair the flexibility and resiliency of the finished stiffener; and acid chemicals were generally faulty both because of their .unstabilizing influence on the nitrocellulose and their noxious or irritating effect on the body.

As a culmination of the foregoing research andinvestigation involving many experiments, I have discovered that boric acid fulfills admirably the various attributes that I have sought in the chemical to be added to the nitrocellulose solution serving as the impregnant for the fibrous base or sheet. When added in finely pulverulent condition and in proper amount to the nitrocellulose solution, the fibrous sheet impregnated with the solution and then dried possesses the various desiderata hereinbefore mentioned, including high residual porosity, substantial fireproofness, and capability of being skived perfectly. The

boric'acid neither tends to, separate out of the nitrocellulose solution nor to filter out on the sur-- face of the fibrous base being impregnated, despite the fact that it exists largely as a suspension in the solution. Again, the boric acid is substantially Without effect on the viscosity of the solution or on the chemical stability of the nitrocellulose appearing as the impregnant in the finished shoe stiifener;- and it does not tend to shed as dust from the stiffener even during cutting or skiving operations; Not only does the finished shoe stiffener have the desired flexibility and resiliency, but its boric acid component is of value therein by reason of its causing a white pigmentation attractive to the shoe-making industry, by reason of "its having a beneficent action on the skin, and by reason of its presenting an antiseptic environment inimical to bacteria or germs such as other:- wise flourish in the perspiration-laden internal region of'th'e shoe fore part. L v I shall now give a specific example of procedure embodying the present invention. The impregnating solution of the present invention may be prepared as a bath containing 28 ounces of nitrocellulose per gallon of suitable volatile 5 nitrocellulose solvent, such as ethyl acetate. The nitrocellulose may advantageously be /;;-second viscosity nitro-cotton, as nitrocellulose of such low viscosity makes for a solution of the desired impregnating fluidity at appropriatelyhighsolute concentration. To the bath of nitrocellulose solution is then added 20 ounces of substantially dry boric acid of commerce per gallon of solution. The boric acid is added in finely pulverulent condition, preferably being of impalpably fine particle size, for instance, a particle size of about 300 or finer mesh. The boric acid is stirred into the solution so as to become substantially uniformly dispersed or suspended therein; and no observable settling or separation of the boric acid from solution occurs even after the solution has been permitted to remain quiescent for days. Through a bath of such a solution containing boric acid suspended therein is passed a suitable fibrous base or sheet, preferably a felt of high porosity and absorptivity, the sheet being completely impregnated with the solution when it emerges from the bath. Such superfluity of solution as is carried by the impregnated sheet may be removed by leading either or both faces oi the sheet as it comes from the bath into contact with doctor or scraper blades, whereupon the impregnated sheet may be dried as by passage through a hot air drying chamber or over' drier drums. The dried impregnated sheet may then be cut into box toe blanks and the blanks skived, as usual, at their margins. Rather than impairing the effectiveness of a skiving knife, I have found that the boric acid component of the stifiener blanks behaves as a lubricant, tending to keep the skiving edge sharp and accurate in its performance.

In making box toe blanks for typical women's shoes, I may to advantage use as the fibrous base a truefelt composed of, say, 20% wool and 80% cotton and weighing about 4 ounces per square yard. Using the cited impregnating composition with such a felt for such purpose, I may produce a dried impregnated sheet weighing 15;, ounces per square yard, that is, a finished sheet containing 10 ounces of impregnating solids, about of which solids is nitrocellulose and about of which is boric acid.

It will be appreciated that the cited example is merely illustrative and is, accordingly, subject to considerable variation. Thus, in the case of box toe stiii'eners intended for usual mens shoes,

the weight of the felt base and its load of impregnating solids may be both greatly increased in approximately the same proportion. Of course, absorbent fibrous bases other than true felts may be employed, e. g., waterlaid felts, ab-

. of nitrocelluose.

sorbent papers, woven or knitted fabrics-etc. It might be further observed that while the niirocellulose content .of the cited impregnating solution might be increased, there is no particular point in so doing, as the composition of the solution cited is one that has desirably high fluidity and at the same time deposits in the base after only a single impregnation and evaporation of the solvent-an appropriate load If the amount of nitrocellulose in solution Ls, on the other hand, materially decreased, the desired toughness, flexibility, and resiliency sought in the stiffener; are not attained in the desired measure. The amount of boric acid cited as being used in the nitrocellulose solution leads to the desired qualities of porosity and fireproofness, in the finishedstiifener. Good results may also be realized with somewhat less than the cited amount of boric acid, but'a large decrease is attended by considerable loss of absorptive and fireproof qualities in the finished stiffener. Because the desired qualities are realized with the cited amount of boric acid, there appears to be no reason for exceeding this amount, since no particular benefit is had, so far as I am now aware, from the excess. The solvent for the nitrocellulose may be other than ethyl acetate, for instance, acetone, butyl acetate, and various glycol derivatives, which may be used either alone or in admixture and, if desired, diluted with suitable amounts of non-solvents, such as benzol or volatile petroleum fractions;

The fireproofing effect of the boric acid is probably attributable to its fusibility at a temperature well below the ignition temperature of both the nitrocellulose and the combustible fiber constituting the base. In fusing, the boric acid not only absorbs a large amount of heat but evidently smothers or envelops the combustible material with which it is associated. In other words, it evidently functions both to cool the combustible material and to exclude atmospheric oxygen from such material. The fact is that when the shoe stiffener of the present invention is exposed to direct flame, for instance, a match flame, it tends merely to char or to burn so reluctantly that the fire stops when the flame is removed. From a practical standpoint, therefore, the stiffener can be regarded as fireproof, since its tendency to ignite and its rate of combustion when ignited is distinctly less than that of even the fibrous base devoid of the highly combustible nitrocellulose.

A surprisin quality of, the shoe stiifener of the present invention is that the boric acid is distributed substantially uniformly throughout the fibrous base along with the nitrocellulose. The ready permeability of the stiffener to nitrocellulose solvents is evidently a reflection of the substantial uniformity with which the boric acid enters into the fibrous base and thus breaks up the continuity of the nitrocellulose film or body deposited in the base. In other words, the particles of boric acid dispersed throughout the body of nitrocellulose occurring in the base evidently constituted myriad loci so highly permeable to nitrocellulose solvent that the solvent immediately diifuses into and throughout the body of nitrocellulose to gelatinize it promptly as a whole and thus to transform the shoe stiffener to the desiredlimp and moldable condition for conformation to a last.

While I am unable to state why particles of boric acid suspended in a nitrocellulose solution tend to enter into and-throughout an absorptive fibrous base that undergoes impregnation with such solution, whereas particles of other chemicals of the same fineness tend to filter out on the surface of the base, it is my theory that the performance of boric acid is a consequence of its tendency to remain stably suspended in the nitrocellulose solution. In this connection, it might be observed that boric acid has a specific gravity of 1.43 and that the particular nitrocellulose solution hereinbefore described not only has a specific gravity (.92) not far removed from that ofthe boric acid but is far more viscous than water, its viscosity at 25 C. being 2050 centipoises or 2300 times that of water. Probably on account of these reasons, the rate of separation of the boric acid from the nitrocellulose solution is so small as to be practically negligible. When an absorptive fibrous base is W6. COMPUEKHIIUNE,

COATING OR FLASH?) lose solution is immediately imbibed by the base,

capillary forces probably causing the solution to diffuse into and throughout the body of the felt. Such capillary forces are evidently powerful enough to sweep the fine particles of boric acid suspended in the solution along with the solution into the internal pores and interstices of the fibrous base, since, as already indicated, the natural or gravitational separatory action on the particles is practically nil. Whether or not my theory or explanation ofthe mechanism underlying the penetration into the fibrous base of the boric acid particles suspended in nitrocellulose solution is correct, it is a fact that such a suspension yields the. satisfactory results hereinbefore described, whereas other chemicals, for instance ones whose specific gravity is several times that of the nitrocellulose solution tend not only to separate outfrom suspension in nitrocellulose solution but also to filter out when impregnation of a fibrous base with the suspension is attempted, yielding an impregnatedsheet whose surface is covered with filtered-Pout solids, which is crackly and dusty on its surface, and which is otherwise unsatisfactory.

The principles of the present invention extend to shoe stiffeners into which nitrocellulose and boric acid are incorporated other than by the particular method hereinbefore described even though such method is simple and economical and hence to be preferred. For instance, shoe stifieners embodying the present invention may contain the nitrocellulose in fibrous, precipitated, or powdered condition, the boric acid being present in powdered or crystalline condition along with the nitrocellulose substantiallythroughout the fibrous base and the stifiener'being quickly permeable to nitrocellulose solvents. Specifically,

may. be cut into stiifener blanks.

W088 HGTGTBHCB QBHFCH HOom 2. A shoe stiffener comprising a fibrous base impregnated throughout with nitrocellulose and containing boric acid interspersed with and throughout said nitrocellulose and existing therewith as a mixed impregnating charge porous to nitrocellulose solvents, said stifiener being readily permeable to nitrocellulose solvents.

3. A shoe stifiener comprising a fibrous base impregnated throughout with nitrocellulose and containing boric acid interspersed with and throughout said nitrocellulose and existing therewith as a mixed impregnating charge porous to nitrocellulose solvents, said stiffener being readily permeable to nitrocellulose solvents and containing suflicient boric acid to render said stiffener diflicultly combustible.

4. A shoe stiffener comprising a fibrous base impregnated throughout with a body of dried nitrocellulose solution and containing boric acid dispersed throughout said nitrocellulose body and serving to break up the continuity of said nitrocellulose body.

5. A shoe stiffener comprising a fibrous base impregnated throughout with a body of dried nitrocellulose solution and containing boric acid dispersed throughout said nitrocellulose body in sufficient amount to retard the normal combustibility thereof and serving to break up the continuity of said nitrocellulose body.

6. A shoe stiffener comprising a fibrous base impregnated throughout with a body of dried nitrocellulose solution and containing boric acid dispersed throughout said nitrocellulose body in suificientamount to render said body difflcultly combustible and serving tobreak up the continuity of said nitrocellulose body, said stiffener being readily permeable to nitrocellulose solvents.

'1. In the manufacture of shoe stifieners, those steps which comprise incorporating throughout a fibrous base both nitrocellulose and boric acid as a substantially uniform interspersion porous deposit therein boric acid and nitrocellulose in' substantially dry admixture with the boric acid being present in suflicient amount to break up the continuity of said nitrocellulose, whereby nitrocellulose solvents can permeate rapidly said impregnated base, and cutting the dried impregnated base into shoe stifiener blanks.

STANLEY P. LOVEIL. 

